Many bacteria regulate virulence factor expression as a function of their population density. This phenomenon, known as 'quorum sensing'(QS), is driven by the detection of a variety of small molecules, collectively referred to as 'autoinducers'(Als). The best characterized Als are the N-acylated L-homoserine lactones (AHLs) utilized by Gram-negative bacteria. The manipulation of AHLs to regulate virulencefactor expression, without exerting selection pressures on the pathogen, is an attractive antimicrobial strategy that has gained considerable attention. However, as the eukaryotic surfaces at which these 'chemical dialogues'between bacteria occurs are also sensitive to these signals, understanding the responses of eukaryotes to AHLs is critical to developing such novel therapeutic strategies. I propose to develop plants as a model system for defining eukaryotic responses to AHLs due to the diverse array of mutants and reporter constructs that are available, their relative ease of genetic manipulation, rapid growth rates, and well defined physiology, as well as their ability to detect and respond to AHLs. In developing this model I intend to exploit recent advances in combinatorial synthesis that have led to the development of a sizeable library of AHL analogues (" 200 compounds). This library will be screened in model plant systems like tobacco, alfalfa, and white clover to identify critical hormonal and physiological responses to a variety of structurally distinct AHLs at multiple time points. AHL responses will be evaluated by both cell-based (protoplast) assays as well as fluorescence microscopy. This two-fold approach permits both high throughput screening as well as tissue localization. Additional studies will evaluate how the perception of select AHLs affects the QS regulatory activity of the root exudate of plants. The results of these studies will be evaluated within the context of their potential impact to the development of QS-regulation as a novel strategy for regulating virulence in bacteria. PUBLIC HEALTH RELEVANCE: The majority of human infections are dependent on a complex 'chemical dialogue'exchanged between bacteria. New antimicrobial strategies, designed around the disruption of these signals, are currently under development and promise to have a substantial impact on human health. However, understanding the responses of host organisms to these bacterial signals is crucial in developing signal disruption as a novel antimicrobial strategy.